linux-kernel - Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been taken exclusively

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Date:   Sun, 1 Oct 2017 16:15:07 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-integrity@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been
 taken exclusively

On Sun, Oct 1, 2017 at 3:34 PM, Dave Chinner <david@...morbit.com> wrote:
>
> We already have a change counter on the inode, which is modified on
> any data or metadata write (i_version) under filesystem locks.  The
> i_version counter has well defined semantics - it's required by
> NFSv4 to increment on any metadata or data change - so we should be
> able to rely on it's behaviour to implement IMA as well.

I actually think i_version has exactly the wrong semantics.

Afaik, it doesn't actually version the file _data_ at all, it only
versions "inode itself changed".

But I might have missed something obvious. The updates are hidden in
some odd places sometimes.

              Linus